Microsoft states that you don't have to uninstall Office 2008 when installing Office 2011, however, I agree with Harry. I have tried it both ways and there is no doubt to me that Office 2011 behaves much better when all remnants of Office 2008 (except documents and user templates) have been removed first.

Hey Everyone,

I have all versions of OSX installed, and all versions of Office 2011/2008. I don't run into any issues when testing with these.

Nonetheless, Office 2011 utilizes OS functions for a lot of its processes, so does Office 2008. For a slower system, it may complicate things.

Do you have AV installed on the Mac? AV can cause corruption in the user files. To reduce this, stop scanning the Microsoft User Data Folder.

Shane Toutges
Microsoft Business Enterprise Support
Office for Mac 2011